1. Field of the Invention
The present invention relates to an image pickup device and an image pickup system, and more particularly those adapted for employing a CMOS area sensor.
2. Related Background Art
Recently, a CMOS area sensor formed by pixels, each including a photodiode and a MOS transistor, has been employed as an image pickup device. The CMOS sensor has advantages, in comparison with a CCD area sensor, of a lower electric power consumption, a lower driving electric power and a possible high-speed operation. The demand for such CMOS area sensor is anticipated to grow hereafter.
The CMOS sensor is constituted of pixels, each formed for example by a photodiode, a floating diffusion region, a transfer transistor for transferring carriers from the photodiode to the floating diffusion region, and a reset transistor for resetting the floating diffusion region to a predetermined potential. A plurality of such pixels are arranged in a matrix to constitute a CMOS area sensor.
In an image pickup device such as a CMOS area sensor, proposals have been made to expand a dynamic range of such a device. For example, Japanese Patent Application Laid-open Nos. 2001-186414 and 2004-335802 propose technologies for expanding the dynamic range of an image pickup device.
However such prior technologies involve a drawback that the image-pickup device often generates noises thereby possibly deteriorating the image quality.